1. Field of the Invention
This disclosure relates to millimeter (mm) wave communication and, more particularly, to a system and method for beam steering signals interrogating a target and receiving replies from the target using circularly polarized waves.
2. Description of the Related Art
Referring to FIG. 1, in a radar interrogation system 50, a processor 54 sends an interrogation message signal 70 through an antenna 52. An interrogation wave 56 is transmitted by antenna 52 typically in the radio frequency range. Interrogation wave 56 may be steered by a beam steerer 58 so that a transmitted wave 60 is directed toward a particular spatial-direction θ because of phase adjustments by beam steerer 58. Wave 60 tends to be polarized in a particular polarization-direction. These may be linear or circularly polarized. Circularly polarized waves may be represented by orthogonal linear polarizations rotating in space and in time quadrature. That is, the electric field of wave 60 may rotate in a first polarization-direction (circular polarization) as wave 60 travels. As shown in the figure, wave 60 may have right hand circular polarization (RHCP)—i.e. from a frame of reference, the electric field rotates clockwise, looking in the spatial-direction of propagation. When wave 60 hits a target 64, wave 60 is partially reflected back as reflected wave 62 toward beam steerer 58 and antenna 52. Reflected wave 62, because of phase reversal in one of the linear components of the reflection, may have an electric field rotating a second polarization-direction opposite the first polarization-direction, counter clockwise, looking in the spatial-direction of propagation, or left hand circularly polarized (LHCP). In the figure, reflected wave 62 is left hand circular polarized. Reflected wave 62 is received by antenna 52, converted into a received signal (not shown) and processed by processor 54. In this way, processor 54 can determine whether target 64 is near antenna 52 at spatial angle θ. This disclosure relates to an improvement over these prior art technologies.